Try this medicated fish food from Dr G. It helps my blue tang to recover from ich after taken this food.
http://www.drgsmarineaquaculture.com/frozen-antiparasitic.cfm
Below is the link for Vinegar Dosing Methodology.
http://reefkeeping.com/joomla/index.php/current-issue/article/116-vinegar-dosing-methodology-for-the-marine-aquarium